Sheet feeding device

ABSTRACT

A sheet feeding device includes a feeding unit that feeds a sheet; a rolling member that rolls by having contact with the sheet being fed by the feeding unit; a supporting member that moves along with a behavior of the sheet with supporting the rolling member so that the rolling member rolls in a feeding direction of the sheet at a predetermined position on the sheet; an acceleration measuring unit that measures accelerations acting on the supporting member in three directions; and a detecting unit that detects a feed error of the sheet based on the accelerations measured by the acceleration measuring unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding device, and moreparticularly, to a sheet feeding device capable of feeding a pluralityof sheets by separating the sheets one by one.

2. Description of the Related Art

A sheet feeding device is generally mounted on an apparatus thatprocesses a plurality of sheets, for example, an image reading apparatussuch as an image scanner, a copier, a facsimile machine, or a characterrecognition device. The sheet feeding device separates stacked sheetsone by one, and sequentially feeds the separated sheet to the imagereading apparatus. Even when a number of sheets are stacked, the imagereading apparatus can process the sheets one by one because the sheetfeeding device automatically feeds the sheets one by one to the imagereading apparatus. However, in such a sheet feeding device, if a feederror occurs while a sheet is being fed, it may cause a damage to thesheet. For example, the sheet may be bent and folded due to the feederror.

A conventional sheet transporting device shown in Japanese PatentApplication Laid-open No. 2007-31104 discloses a pair of vibratingmembers, an acceleration sensing unit, and a feed-error detecting unit.The vibrating members are arranged in a width direction of a sheet path,and respectively receive a vibration of a sheet being fed. Theacceleration sensing unit senses each of the vibrations transmitted tothe vibrating members. The feed-error detecting unit detects a feederror of the sheet based on the vibrations sensed by the accelerationsensing unit. If the sheet is fed properly, i.e., if the sheet is notfed askew, the acceleration sensing unit senses the vibrationstransmitted to the vibrating members simultaneously, so that outputsignals from the acceleration sensing unit overlap each other as thepeaks in the same timing. On the other hand, if the sheet is fed askew,output signals from the acceleration sensing unit form two peaks in thetransport of one sheet, whereby the sheet transporting device can detecta skew of the sheet.

However, the conventional sheet transporting device needs to include aplurality of the acceleration sensing units and the vibrating members tocope with a plurality of types of feed errors occurring while a sheet isfed. Such feed errors include a so-called cumulative skew caused by arotation or deformation of a sheet being fed and a jam caused by upliftof a sheet or the like. Therefore, there has been a need of a sheetfeeding device capable of detecting a plurality of types of feed errorsbefore a damage to a sheet occurs with a simple configuration.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

According to an aspect of the present invention, a sheet feeding deviceincludes a feeding unit that feeds a sheet; a rolling member that rollsby having contact with the sheet being fed by the feeding unit; asupporting member that moves along with a behavior of the sheet withsupporting the rolling member so that the rolling member rolls in afeeding direction of the sheet at a predetermined position on the sheet;an acceleration measuring unit that measures accelerations acting on thesupporting member in three directions; and a detecting unit that detectsa feed error of the sheet based on the accelerations measured by theacceleration measuring unit.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a sheet feeding device according to a firstembodiment of the present invention;

FIG. 2 is a plan view of the sheet feeding device according to the firstembodiment;

FIG. 3 is a side view of the sheet feeding device according to the firstembodiment;

FIG. 4A is a plan view of an acceleration detecting unit according tothe first embodiment;

FIG. 4B is a front view of the acceleration detecting unit according tothe first embodiment;

FIG. 4C is a side view of the acceleration detecting unit according tothe first embodiment;

FIG. 5 is a plan view of the sheet feeding device according to the firstembodiment for explaining an operation of the acceleration detectingunit;

FIG. 6 is a side view of the sheet feeding device according to the firstembodiment for explaining an operation of the acceleration detectingunit;

FIG. 7 is a flowchart of a feed-error detecting process performed by thesheet feeding device according to the first embodiment;

FIG. 8A is a plan view of an acceleration detecting unit of a sheetfeeding device according to a second embodiment of the presentinvention;

FIG. 8B is a front view of the acceleration detecting unit according tothe second embodiment;

FIG. 8C is a side view of the acceleration detecting unit according tothe second embodiment;

FIG. 9 is a plan view of a sheet feeding device according to a thirdembodiment of the present invention;

FIG. 10 is a side view of the sheet feeding device according to thethird embodiment;

FIG. 11 is a block diagram of a sheet feeding device according to afourth embodiment of the present invention;

FIG. 12 is a perspective view of an acceleration detecting unit of thesheet feeding device according to the fourth embodiment;

FIG. 13 is a graph of an example of an acceleration waveform when nofeed error occurs in the sheet feeding device according to the fourthembodiment;

FIG. 14 is a graph of an example of an acceleration waveform when a feederror occurs in the sheet feeding device according to the fourthembodiment; and

FIG. 15 is a flowchart of a feed-error detecting process performed bythe sheet feeding device according to the fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are explained in detailbelow with reference to the accompanying drawings.

A sheet feeding device 1 according to a first embodiment of the presentinvention is explained in detail below with reference to FIGS. 1 to 7.

FIG. 1 is a block diagram of the sheet feeding device 1. FIG. 2 is aplan view of the sheet feeding device 1. FIG. 3 is a side view of thesheet feeding device 1. The sheet feeding device 1 automatically feedsstacked sheets S as sheet-like media by separating the sheet S one byone as shown in FIGS. 1 to 3.

It is assumed that the sheet feeding device 1 is mounted on an imagereading apparatus capable of processing a plurality of sheets S, such asan image scanner, a copying machine, a facsimile machine, or a characterrecognition device. The sheet feeding device 1 separates stacked sheetsS one by one, and sequentially feeds the separated sheet S to the imagereading apparatus.

The sheet feeding device 1 automatically and sequentially feeds aplurality of sizes and a massive amount of sheets S to a conveying unit(not shown) of the image reading apparatus. The sheet feeding device 1includes a hopper 2 as a sheet stacking unit, a separate-feeding unit 3as a feeding unit, and a control unit 4.

Incidentally, a direction of which a sheet S is fed by the sheet feedingdevice 1 is referred to as a “feeding direction Y”, a directionhorizontally-perpendicular to the feeding direction Y is referred to asa “width direction X”, and a direction perpendicular to both the feedingdirection Y and the width direction X is referred to as a “heightdirection Z”.

The separate-feeding unit 3 automatically and sequentially feeds sheetsS stacked on the hopper 2 by separating the sheet S one by one. Theconveying unit of the image reading apparatus is located on thedownstream side of the separate-feeding unit 3 in the feeding directionY.

The conveying unit is included in the image reading apparatus on whichthe sheet feeding device 1 is mounted, and conveys a sheet S fed fromthe sheet feeding device 1 to any of units included in the image readingapparatus. For example, an optical unit as an image reading unit isprovided on a sheet conveying path of the conveying unit. While a sheetS is conveyed on the sheet conveying path by the conveying unit, theoptical unit reads out an image on the sheet S. The conveying unitincludes, for example, a drive roller (not shown) and a driven roller(not shown). The drive roller is driven to rotate around a central axisas a rotating shaft by a drive force from a drive source (not shown). Bya rotation transmission from the drive roller, the driven roller rotatesaround a central axis as a rotating shaft in accordance with therotation of the drive roller. The drive roller and the driven roller arearranged to be opposed to each other along the width direction X. Thedriven roller is pressed (or biased) towards the drive roller by abiasing unit (not shown) to have contact with the drive roller. With thebias applied to the driven roller, a sheet S is sandwiched between anouter circumferential surface of the drive roller and an outercircumferential surface of the driven roller. A plurality of such driverollers (not shown) and a plurality of such driven rollers (not shown)are provided along the sheet conveying path. As the drive rollers aredriven to rotate, the sheet S is passed between the drive rollers andthe driven rollers sequentially, and conveyed to any of the units in theimage reading apparatus, for example, the optical unit.

The hopper 2 has a substantially rectangular stacking surface 21. Aplurality of sheets S is stacked on the stacking surface 21. The stackedsheets S are pressed towards the stacking surface 21 by a biasing unit(not shown). The hopper 2 includes a hopper lifting mechanism (notshown) so that the hopper 2 is lifted up and down in the heightdirection Z depending on the quantity of sheets S stacked on thestacking surface 21.

The separate-feeding unit 3 employs an uppermost-sheet feeding method.The separate-feeding unit 3 includes a separation roller 31 and a brakeroller 32. The separation roller 31, as a separating unit, separates asheet S placed on the top of the sheets S stacked on the stackingsurface 21 (hereinafter, “the top sheet S”) from the sheets S and feedsthe sheets S one by one. The brake roller 32 constrains the sheets Sother than the top sheet S having direct contact with the separationroller 31 not to be fed along with the top or uppermost sheet S.

The separation roller 31 is made of a material with a large frictionalforce (or high coefficient of friction) such as a foamed rubber, and hasa cylindrical shape. A central axis of the separation roller 31 is setup to be parallel to the width direction X, i.e., in a directionperpendicular to the feeding direction Y along the stacking surface 21.In addition, the separation roller 31 is set up in such a way that thecentral axis of the separation roller 31 is located above an uppersurface of the hopper 2 (above the stacking surface 21), and apredetermined distance is kept between an outer circumferential surfaceof the separation roller 31 and the stacking surface 21 in the heightdirection Z. The hopper 2 is set up in such a way that sheets S arestacked on the stacking surface 21 so that trailing edges (edges on theupstream side in the feeding direction Y) of the sheets S are located onthe upstream side of the separation roller 31 in the feeding directionY. As the hopper 2 is lifted up in the height direction Z, the hopper 2and the separation roller 31 get closer to each other. As the hopper 2is lifted down in the height direction Z, the hopper 2 and theseparation roller 31 get further away from each other.

The separation roller 31 is connected to a drive motor 31 a as a drivingunit via a transmission gear (not shown) and a belt (not shown). Theseparation roller 31 is driven to rotate around the central axis as arotating shaft by the application of a rotation drive force from thedrive motor 31 a. The separation roller 31 is driven to rotate in a pickdirection, i.e., a direction of which the outer circumferential surfaceof the separation roller 31 rolls to the downstream side in the feedingdirection Y on the stacking surface 21.

The brake roller 32 has a cylindrical shape with the almost same lengthas that of the separation roller 31. In the same manner as theseparation roller 31, a central axis of the brake roller 32 is set up tobe horizontally perpendicular to the feeding direction Y, i.e., alongthe width direction X. The brake roller 32 rotates around the centralaxis as a rotating shaft. The brake roller 32 is arranged to be opposedto the separation roller 31. The central axis of the brake roller 32 isset up to be located between the central axis of the separation roller31 and the stacking surface 21 in the height direction Z. The brakeroller 32 is pressed (or biased) towards the separation roller 31 by abiasing unit (not shown) to have contact with the separation roller 31.By a rotation transmission from the separation roller 31, the brakeroller 32 rotates around the central axis as a rotating shaft inaccordance with the rotation of the separation roller 31 in such adirection that an outer circumferential surface of the brake roller 32rolls to the downstream side in the feeding direction Y at a contactportion where the brake roller 32 has contact with the separation roller31. In the first embodiment, the brake roller 32 is biased towards theseparation roller 31 by the biasing unit. Alternatively, the brakeroller 32 can be driven to rotate in a direction opposite to therotating direction of the separation roller 31 instead of providing thebiasing unit.

The control unit 4 includes a microcomputer, and controls the sheetfeeding device 1. The control unit 4 is connected to the drive motor 31a, and further electrically connected to an empty sensor (not shown), asheet sensor (not shown), and the like. The empty sensor is used todetect whether there is any sheet S which trailing edge is located onthe upstream side of the separation roller 31 on the stacking surface21. The sheet sensor is used to detect the quantity of sheets S stackedon the stacking surface 21. As the empty sensor and the sheet sensor,for example, a photo sensor using an infrared radiation or the like canbe used. The empty sensor and the sheet sensor respectively transmit asensed signal indicating a result of the detection to the control unit4.

In the sheet feeding device 1, the separation roller 31 is driven torotate in the pick direction, so that the top sheet S can be picked upfrom sheets S stacked on the stacking surface 21 located on the upstreamside of the separation roller 31 on the outer circumferential surface ofthe separation roller 31, and fed to the downstream side in the feedingdirection Y (to the side of the conveying unit of the image readingapparatus). When the top sheet S is fed by the separation roller 31, itmay happen that a sheet S other than the top sheet S (for example, asheet S located beneath the top sheet S) is also fed to the downstreamside in the feeding direction Y along with the top sheet S due to africtional force generated between the sheets S. However, in the sheetfeeding device 1, the sheet S fed along with the top sheet S can beseparated from the top sheet S by the brake roller 32.

Namely, while a leading edge of the top sheet S is held between theseparation roller 31 and the brake roller 32, the sheet S fed along withthe top sheet S is constrained not to be fed to the downstream side inthe feeding direction Y by having contact with the brake roller 32,i.e., the sheet S fed along with the top sheet S is stopped at theupstream side of the brake roller 32. After the top sheet S is fed tothe downstream side in accordance with the rotation of the separationroller 31, a leading edge of the sheet S stopped at the upstream side ofthe brake roller 32 is subsequently held between the separation roller31 and the brake roller 32, and then fed to the downstream side inaccordance with the rotation of the separation roller 31. The hopper 2is lifted up in the height direction Z depending on the quantity ofsheets S stacked on the stacking surface 21. In this manner, the sheet Sfed along with the top sheet S is separated from the top sheet S by theseparation roller 31 and the brake roller 32, and only the top sheet Sis fed to the conveying unit one by one sequentially. This means theuppermost-sheet feeding method.

When a feed error occurs while a sheet S is fed, it may cause a damageto the sheet S, for example, the sheet may be bent and folded.

To cope with the problems, the sheet feeding device 1 is configured todetect a feed error of a sheet S based on accelerations acting on aroller supporting mechanism in three directions (or dimensions).Therefore, the sheet feeding device 1 can detect a plurality of types offeed errors before any damage to a sheet S occurs with a simpleconfiguration. Incidentally, a detection of a feed error by the sheetfeeding device 1 also includes a forecast of a feed error before thefeed error occurs, so that it is possible to prevent a sheet S from adamage due to the feed error.

Specifically, the sheet feeding device 1 further includes anacceleration detecting unit 5 as shown in FIGS. 1 to 3. Moreover, thecontrol unit 4 includes a processing unit 41, a storing unit 42, and aninput/output unit 43. The acceleration detecting unit 5 includes afollowing roller 6, a roller supporting mechanism 7, and a three-axisaccelerometer 8. The following roller 6 rolls by having contact with asheet S being fed. The roller supporting mechanism 7 supports thefollowing roller 6, and is capable of moving and rotating along with abehavior of the sheet S together with the following roller 6. Thethree-axis accelerometer 8 measures an acceleration acting on the rollersupporting mechanism 7.

The following roller 6 has a cylindrical shape, and a rotating shaft ofthe following roller 6 is arranged along the width direction X. Thefollowing roller 6 is arranged at the almost same level of theseparation roller 31 in the height direction Z and on the upstream sideof the separation roller 31 in the feeding direction Y. When the topsheet S is fed by the separate-feeding unit 3, the following roller 6rolls by having line contact with the top sheet S on a line along thewidth direction X at the upstream side of the separate-feeding unit 3.The following roller 6, the separation roller 31, and the brake roller32 are arranged on a center line of the properly-fed sheet S in thewidth direction X. In addition, the rotating shafts of the followingroller 6, the separation roller 31, and the brake roller 32 are arrangedsubstantially parallel to one another.

FIGS. 4A to 4C are respectively a plan view, a front view, and a sideview of the acceleration detecting unit 5. As shown in FIGS. 4A to 4C,the roller supporting mechanism 7 rotatably supports the followingroller 6 so that the following roller 6 can roll in the feedingdirection Y at a predetermined position. The roller supporting mechanism7 can move in the height direction Z and rotate around an axis along theheight direction Z along with a behavior of the sheet S, at least. Theroller supporting mechanism 7 includes a roller support shaft 71, abracket 72, a pair of roller supporting members 73, a roller-sidecoupling member 74, and a supporting-member-side coupling member 75.

The roller support shaft 71 is arranged along the width direction X, andserves as the rotating shaft of the following roller 6. The bracket 72has a concave portion opened downward (to the side of the sheet S). Bothends of the roller support shaft 71 are fixed on an inner surface of theconcave portion. The rotating shaft of the following roller 6 isrotatably supported by the bracket 72 via the roller support shaft 71.The roller-side coupling member 74 is arranged on an upper outer surfaceof the concave portion (on a surface opposite to the side of the sheetS). The roller-side coupling member 74 includes a pair of couplingplates 74 a and 74 b. The coupling plates 74 a and 74 b are arranged insuch a way that a side surface of each of the coupling plates 74 a and74 b is faced to each other on the upper outer surface of the bracket72, and extend along the width direction X to be opposed to each other.The coupling plate 74 a is located on the downstream side, and thecoupling plate 74 b is located on the upstream side in the feedingdirection Y.

The roller supporting members 73 are arranged to be parallel to eachother in the feeding direction Y with keeping a predetermined distancein the width direction X between the roller supporting members 73. Theroller supporting members 73 respectively include, for example, a memberwith a certain elastic force such as a plate spring so as to return thefollowing roller 6 back to an initial position. Each of the rollersupporting members 73 includes a base-end support shaft 76 at its baseend portion located on the upstream side in the feeding direction Y anda leading-end support shaft 77 at its leading end portion located on thedownstream side in the feeding direction Y. The base-end support shaft76 and the leading-end support shaft 77 are arranged to be parallel toeach other in the width direction X. The supporting-member-side couplingmember 75 is rotatably attached to the leading end portion of each ofthe roller supporting members 73 via the leading-end support shaft 77.The supporting-member-side coupling member 75 and the roller-sidecoupling member 74 are rotatably coupled to each other via afeeding-directional shaft 78 so that the supporting-member-side couplingmember 75 and the roller-side coupling member 74 can rotaterespectively. The feeding-directional shaft 78 is arranged to beparallel to the feeding direction Y. The feeding-directional shaft 78and the supporting-member-side coupling member 75 are arranged betweenthe coupling plates 74 a and 74 b in the feeding direction Y. The baseend portion of each of the roller supporting members 73 is supported bya casing (not shown) of the sheet feeding device 1 via the base-endsupport shaft 76.

The entire roller supporting mechanism 7 can rotate around the base-endsupport shaft 76, i.e., around an axis in the width direction X togetherwith the following roller 6. In addition, the entire roller supportingmechanism 7 can also rotate around the base end portion in the heightdirection Z together with the following roller 6 by the action of areaction force to the elastic force of the roller supporting members 73.At this time, the following roller 6 supported by the bracket 72 canroll around the roller support shaft 71, and also the bracket 72 canrotate around the feeding-directional shaft 78, i.e., around an axis inthe feeding direction Y together with the following roller 6. Therefore,the roller supporting mechanism 7 can move along with a behavior of thesheet S fed by the separate-feeding unit 3 with supporting the followingroller 6 so that the following roller 6 rolls in the feeding direction Yat the predetermined position. In other words, when there is any changein a behavior of the sheet S fed by the separate-feeding unit 3, thefollowing roller 6 and the roller supporting mechanism 7 can move(rotate) along with the behavior of the sheet S.

As the three-axis accelerometer 8, any types of accelerometers, such asan electrostatic capacitive accelerometer and a piezoelectricaccelerometer, can be used. In the first embodiment, a completethree-axis accelerometer manufactured by Analog Devices Inc. is used asthe three-axis accelerometer 8. The three-axis accelerometer 8 canmeasure not only a static acceleration such as a gravity but also adynamic acceleration such as a movement, impact, and vibration. Thethree-axis accelerometer 8 can measure an acceleration acting on thethree-axis accelerometer 8 itself, and capture a gravity as theacceleration, and also detect a tilt of an object on which thethree-axis accelerometer 8 is mounted. The three-axis accelerometer 8can measure an acceleration, for example, in the range of 1 G to 3 G.

The three-axis accelerometer 8 is provided on the coupling plate 74 a,and simultaneously measures accelerations Gx, Gy, and Gz that act on theroller supporting mechanism 7 in the width direction X, the feedingdirection Y, and the height direction Z, respectively. A samplinginterval (an interval between data acquisitions) of each of theaccelerations Gx, Gy, and Gz measured by the three-axis accelerometer 8is set up to a relatively short interval but a sufficient interval tocope with a moving (rotating) speed of the following roller 6 and theroller supporting mechanism 7 for moving (rotating) along with the sheetS, i.e., a time to get the following roller 6 and the roller supportingmechanism 7 to move (rotate) along with the sheet S in accordance with achange in a behavior of the sheet S being fed. The sampling interval isset up to, for example, about 0.1 second to 0.25 second. When there isany change in the behavior of the sheet S being fed by theseparate-feeding unit 3, the three-axis accelerometer 8 can reliablymeasure an acceleration acting on the following roller 6 and the rollersupporting mechanism 7, which move (rotate) along with the behavior ofthe sheet S, by dividing the acceleration into three components ofaccelerations in three directions, i.e., accelerations Gx, Gy, and Gz.In other words, by sensing behaviors of the following roller 6 and theroller supporting mechanism 7, the three-axis accelerometer 8 canindirectly sense a behavior of the sheet S via the following roller 6and the roller supporting mechanism 7. The three-axis accelerometer 8 iselectrically connected to the control unit 4, and outputs the measuredaccelerations Gx, Gy, and Gz to the control unit 4.

The control unit 4 includes a computer such as a personal computer. Asshown in FIG. 1, in the control unit 4, the processing unit 41 and thestoring unit 42 are connected to each other. Furthermore, the drivemotor 31 a and the three-axis accelerometer 8 are connected to theprocessing unit 41 via the input/output unit 43.

The storing unit 42 stores therein a computer software program executinga feed-error detecting process performed by the sheet feeding device 1.The storing unit 42 is composed of any of a hard disk drive, amagneto-optical disk device, a nonvolatile memory (a read-only memorymedium) such as a compact disk read-only memory (CD-ROM) or a flashmemory, and a volatile memory such as a random access memory (RAM)either alone or in combination.

The computer software program can be combined with other computersoftware program, which is stored in a computer system in advance, so asto perform the feed-error detecting method. Alternatively, the computersoftware program capable of exercising a function of the processing unit41 can be stored in a computer-readable recording medium so that thecomputer system can read the computer software program from therecording medium to execute a feed-error detecting process with thefeed-error detecting method. Incidentally, it is assumed that the“computer system” includes an operating system (OS) and hardware such asa peripheral device. The storing unit 42 can be either built in theprocessing unit 41 or included in other devices (for example, a databaseserver).

The processing unit 41 includes a memory (not shown) and a centralprocessing unit (CPU) (not shown). When the feed-error detecting processis executed, the processing unit 41 calculates a value by reading thecomputer software program into the memory in accordance withpredetermined procedures of the feed-error detecting method. At thistime, the processing unit 41 arbitrarily stores the calculated valueobtained in midstream of the calculation in the storing unit 42, andkeeps performing the calculation with the value fetched out from thestoring unit 42. Alternatively, such a function of the processing unit41 can be exercised with a dedicated hardware instead of the computersoftware program.

As shown in FIG. 1, the processing unit 41 includes an error detectingunit 44, a counting unit 45, and a feeding stop unit 46.

The error detecting unit 44 detects a feed error of the sheet S based onaccelerations Gx, Gy, and Gz measured by the three-axis accelerometer 8.When an increase or decrease of any of the accelerations Gy and Gx iscontinued for a predetermined time period, the error detecting unit 44detects a skew (a cumulative skew) of the sheet S as a feed error of thesheet S.

For example, as shown in FIG. 2, when the sheet S is fed properly by theseparate-feeding unit 3, the following roller 6 supported by the rollersupporting mechanism 7 rolls with having contact with the sheet S beingproperly fed in the feeding direction Y at the same position in anidling manner. Namely, although the sheet S is fed in the feedingdirection Y, the following roller 6 is supported by the rollersupporting mechanism 7 at the predetermined position, so that thefollowing roller 6 rolls in the idling manner at the predeterminedposition. At this time, although the following roller 6 rolls, thethree-axis accelerometer 8 does not rotate because the three-axisaccelerometer 8 is provided not directly to the following roller 6 butto the roller supporting mechanism 7. Therefore, no acceleration acts onthe three-axis accelerometer 8 in any direction, so that the three-axisaccelerometer 8 senses no change in each of the accelerations Gx, Gy,and Gz. In other words, the accelerations Gx, Gy, and Gz are all zero.

On the other hand, for example, as shown in FIG. 5, when the sheet S isskewed while the sheet S is being fed by the separate-feeding unit 3,there is a change in a behavior of the sheet S due to an occurrence of acumulative skew of the sheet S. A moment of rotation around an axis inthe height direction Z acts on the following roller 6 having linecontact with the sheet S on a line along the width direction X and theroller supporting mechanism 7 supporting the following roller 6. Themoment of rotation acts as a reaction force to the elastic force of theroller supporting members 73, so that the roller supporting mechanism 7rotates around the base end portions of the roller supporting members 73in the height direction Z along with the behavior of the sheet Stogether with the following roller 6. At this time, the three-axisaccelerometer 8 measures an acceleration acting on the three-axisaccelerometer 8 in accordance with the rotation around the axis in theheight direction Z by dividing the acceleration into accelerations Gxand Gy as components of accelerations in the width direction X and thefeeding direction Y. The error detecting unit 44 can detect a skew (acumulative skew) of the sheet S as a feed error of the sheet S based oneither one or both of the accelerations Gx and Gy.

When an increase or decrease of an acceleration Gz is continued for apredetermined time period, the error detecting unit 44 detects a jam asa feed error of the sheet S. In this case, the detection of a jam by theerror detecting unit 44 indicates that the error detecting unit 44forecasts an occurrence of a jam before the jam occurs so as to preventa damage to the sheet S from occurring. For example, as shown in FIG. 6,when the sheet S is lifted up while the sheet S is being fed by theseparate-feeding unit 3, there is a change in a behavior of the sheet Sdue to an occurrence of a jam caused by the uplift of the sheet S. Aforce generated by the uplift of the sheet S acts on the followingroller 6 having contact with the sheet S and the roller supportingmechanism 7 supporting the following roller 6. By the action of theforce, the roller supporting mechanism 7 rotates around the base-endsupport shaft 76, i.e., around the axis in the width direction Xtogether with the following roller 6 along with the behavior of thesheet S. At this time, the three-axis accelerometer 8 measures anacceleration acting on the three-axis accelerometer 8 in accordance withthe rotation around the base-end support shaft 76 (the axis in the widthdirection X) by dividing the acceleration into accelerations Gy and Gzas components of accelerations in the feeding direction Y and the heightdirection Z. The error detecting unit 44 can forecast an occurrence of ajam before the jam occurs as a feed error of the sheet S based on theacceleration Gz.

In this manner, with only one sensor, i.e., the three-axis accelerometer8, behaviors of the following roller 6 and the roller supportingmechanism 7 can be sensed, and thereby sensing a behavior of the sheet Sindirectly. Therefore, the sheet feeding device 1 can detect a pluralityof types of feed errors separately with a compact and simpleconfiguration.

Incidentally, the error detecting unit 44 is configured to detect a skewor forecast an occurrence of a jam only when an increase or decrease ofan acceleration sensed by the three-axis accelerometer 8 is continuedfor the predetermined time period. This is to prevent the errordetecting unit 44 from detecting a skew or forecasting an occurrence ofa jam by mistake. In other words, a feed error is detected based on nota momentary measurement value of an acceleration measured by thethree-axis accelerometer 8 but an amount of temporal change in theacceleration for the predetermined time period. Therefore, it ispossible to eliminate the effect of noise, and thereby preventing afalse detection. In addition, it is possible to grasp a status of a feederror in more detail. The predetermined time period can be arbitrarilyset up depending on the sensitivity of detection of a skew or forecastof an occurrence of a jam.

Furthermore, the reason why the error detecting unit 44 is configured todetect a skew or forecast an occurrence of a jam only when an increaseor decrease of an acceleration sensed by the three-axis accelerometer 8is continued for the predetermined time period is that a measurementvalue of the acceleration output from the three-axis accelerometer 8varies either positive or negative oppositely depending on a directionof action of the acceleration. For example, a measurement value of theacceleration varies either positive or negative oppositely depending onwhether an acceleration in the width direction X acts on the left orright side toward the downstream side in the feeding direction Y.Therefore, when an increase or decrease of an acceleration is continued,it indicates that the acceleration, for example, in the width directionX continuously acts on either side. Unless otherwise noted, a case wherea skew or a jam is detected by a continuous increase of an accelerationis explained below. Although an explanation about a case of a continuousdecrease of an acceleration is omitted, a skew or a jam can be detectedby a continuous decrease of an acceleration in about the same manner asthe case of the continuous increase.

When an increase or decrease of each of components of accelerations inthe width direction X, the feeding direction Y, and the height directionZ is continued based on accelerations Gx, Gy, and Gz measured by thethree-axis accelerometer 8, i.e., when a previously-measuredacceleration increases and a currently-measured acceleration alsoincreases or the previously-measured acceleration decreases and thecurrently-measured acceleration also decreases, the counting unit 45increments a value of a counter for the acceleration by one. When thevalue reaches or exceeds a threshold, i.e., when the increase ordecrease of the acceleration is continued for the predetermined timeperiod, the error detecting unit 44 detects a skew or a jam. The feedingstop unit 46 stops the feeding of the sheet S by the separate-feedingunit 3 depending on a result of the detection by the error detectingunit 44. If the feeding of the sheet S is continued even though a skewor a jam is detected, it may cause a damage to the sheet S. Therefore,when the error detecting unit 44 detects a feed error of the sheet S,the feeding stop unit 46 controls the drive motor 31 a to stop drivingthe separation roller 31 so that the feeding of the sheet S is stopped.Consequently, it is possible to prevent a damage to the sheet S fromoccurring.

A feed-error detecting process performed by the sheet feeding device 1is explained in detail below with reference to a flowchart shown in FIG.7. The control unit 4 determines whether a sheet S is being fed at thismoment (Step S100). If the sheet S is not being fed at this moment (NOat Step S100), the counting unit 45 clears all values of each ofcounters for accelerations in each direction, and the feed-errordetecting process is terminated as a normal end. If the sheet S is beingfed at this moment (YES at Step S100), the control unit 4 acquiresaccelerations Gx, Gy, and Gz respectively in the width direction X, thefeeding direction Y, and the height direction Z that are measured atpredetermined sampling intervals by the three-axis accelerometer 8 (StepS102), and stores the acquired accelerations Gx, Gy, and Gz in a timetrace buffer (not shown) of the storing unit 42 (Step S104).

The control unit 4 compares the currently-acquired accelerations Gx, Gy,and Gz with previously-acquired accelerations Gx, Gy, and Gz (StepS106), and the counting unit 45 determines whether thecurrently-acquired acceleration Gz increases (or decreases) as comparedwith the previously-acquired acceleration Gz (Step S108). If it isdetermined that the acceleration Gz increases (or decreases) (YES atStep S108), the counting unit 45 increments a value of a counter for theacceleration Gz by one. The error detecting unit 44 determines whetherthe increase (or decrease) of the acceleration Gz is continued for thepredetermined time period based on whether the incremented value of thecounter for the acceleration Gz reaches or exceeds a threshold (StepS110). If the error detecting unit 44 determines that the increase (ordecrease) of the acceleration Gz is continued for the predetermined timeperiod (YES at Step S110), and forecasts an occurrence of a jam causedby uplift of the sheet S, as error processes, the control unit 4 informsa user of an error, and the feeding stop unit 46 stops the feeding ofthe sheet S (Step S112). Then, the feed-error detecting process isterminated as an abnormal end.

If it is determined that the acceleration Gz does not increase (ordecrease) (NO at Step S108), or if it is determined that the increase(or decrease) of the acceleration Gz is not continued for thepredetermined time period (NO at Step S110), the counting unit 45determines whether the currently-acquired acceleration Gy increases (ordecreases) as compared with the previously-acquired acceleration Gy(Step S114). If it is determined that the acceleration Gy increases (ordecreases) (YES at Step S114), the counting unit 45 increments a valueof a counter for the acceleration Gy by one. The error detecting unit 44determines whether the increase (or decrease) of the acceleration Gy iscontinued for the predetermined time period based on whether theincremented value of the counter for the acceleration Gy reaches orexceeds a threshold (Step S116). If the error detecting unit 44determines that the increase (or decrease) of the acceleration Gy iscontinued for the predetermined time period (YES at Step S116), anddetects a skew of the sheet S, as error processes, the control unit 4informs a user of an error, and the feeding stop unit 46 stops thefeeding of the sheet S (Step S118). Then, the feed-error detectingprocess is terminated as the abnormal end.

If it is determined that the acceleration Gy does not increase (ordecrease) (NO at Step S114), or it is determined that the increase (ordecrease) of the acceleration Gy is not continued for the predeterminedtime period (NO at Step S116), the counting unit 45 determines whetherthe currently-acquired acceleration Gx increases (or decreases) ascompared with the previously-acquired acceleration Gx (Step S120). If itis determined that the acceleration Gx increases (or decreases) (YES atStep S120), the counting unit 45 increments a value of a counter for theacceleration Gx by one. The error detecting unit 44 determines whetherthe increase (or decrease) of the acceleration Gx is continued for thepredetermined time period based on whether the incremented value of thecounter for the acceleration Gx reaches or exceeds a threshold (StepS122). If the error detecting unit 44 determines that the increase (ordecrease) of the acceleration Gx is continued for the predetermined timeperiod (YES at Step S122), and detects a skew of the sheet S, as errorprocesses, the control unit 4 informs a user of an error, and thefeeding stop unit 46 stops the feeding of the sheet S (Step S124). Then,the feed-error detecting process is terminated as the abnormal end. Ifit is determined that the acceleration Gx does not increase (ordecrease) (NO at Step S120), or it is determined that the increase (ordecrease) of the acceleration Gx is not continued for the predeterminedtime period (NO at Step S122), the process control returns to Step S100.

In this manner, the sheet feeding device 1 includes the following roller6 capable of rolling by having line contact with a sheet S fed by theseparate-feeding unit 3 on a line along the width direction X of thesheet S, the roller supporting mechanism 7 that supports the followingroller 6 so that the following roller 6 can roll in the feedingdirection Y at the predetermined position on the sheet S, and is capableof moving and rotating along with a behavior of the sheet S fed by theseparate-feeding unit 3 together with the following roller 6, thethree-axis accelerometer 8 capable of measuring accelerations in threedirections acting on the roller supporting mechanism 7, and the errordetecting unit 44 that detects a feed error of the sheet S based on theaccelerations measured by the three-axis accelerometer 8.

Specifically, the error detecting unit 44 detects a feed error of thesheet S based on accelerations Gx, Gy, and Gz in the width direction X,the feeding direction Y, and the height direction Z, respectively, whichact on the roller supporting mechanism 7 capable of moving and rotatingalong with a behavior of the sheet S together with the following roller6. In this manner, with only one sensor, i.e., the three-axisaccelerometer 8, behaviors of the following roller 6 and the rollersupporting mechanism 7 can be sensed, and thereby sensing a behavior ofthe sheet S indirectly. Therefore, the sheet feeding device 1 can detecta plurality of types of feed errors separately with a compact and simpleconfiguration.

Furthermore, the three-axis accelerometer 8 can measure accelerations inthe feeding direction Y, the width direction Xhorizontally-perpendicular to the feeding direction Y, and the heightdirection Z perpendicular to both the feeding direction Y and the widthdirection X. The roller supporting mechanism 7 can move in the heightdirection Z, and rotate around an axis in the height direction Z alongwith a behavior of the sheet S. Therefore, when there is any change inthe behavior of the sheet S due to an occurrence of a cumulative skew ofthe sheet S, and a moment of rotation around the axis in the heightdirection Z acts on the following roller 6 and the roller supportingmechanism 7, the roller supporting mechanism 7 rotates around the axisin the height direction Z together with the following roller 6. At thistime, the three-axis accelerometer 8 measures an acceleration acting onthe three-axis accelerometer 8 in accordance with the rotation aroundthe axis the height direction Z by dividing the acceleration intoaccelerations Gx and Gy in the width direction X and the feedingdirection Y, respectively. Therefore, a skew of the sheet S as a feederror of the sheet S can be detected based on the accelerations Gx andGy. When there is any change in the behavior of the sheet S due to anoccurrence of a jam caused by uplift of the sheet S, and a forcegenerated by the uplift of the sheet S acts on the following roller 6and the roller supporting mechanism 7, the roller supporting mechanism 7moves in the height direction Z along with the behavior of the sheet Stogether with the following roller 6. At this time, the three-axisaccelerometer 8 measures an acceleration acting on the three-axisaccelerometer 8 in accordance with the movement in the height directionZ by dividing the acceleration into accelerations Gy and Gz in thefeeding direction Y and the height direction Z, respectively. Therefore,an occurrence of a jam as a feed error of the sheet S can be forecastedbefore the jam occurs based on the acceleration Gz.

Moreover, when an increase or decrease of any of accelerations Gy and Gxrespectively in the feeding direction Y and the width direction X iscontinued for the predetermined time period, the error detecting unit 44detects a skew of the sheet S as a feed error of the sheet S. Therefore,it is possible to eliminate the effect of noise, and thereby preventinga false detection of the skew.

Furthermore, when an increase or decrease of an acceleration Gz in theheight direction Z is continued for the predetermined time period, theerror detecting unit 44 forecasts an occurrence of a jam as a feed errorof the sheet S. Therefore, it is possible to eliminate the effect ofnoise, and thereby preventing a false forecast of the jam.

Moreover, the following roller 6 has a cylindrical shape, and a rotatingshaft of the following roller 6 is arranged along the width direction X.Therefore, when a sheet S is fed by the separate-feeding unit 3, thefollowing roller 6 can roll by having line contact with the sheet S on aline along the width direction X.

Furthermore, the sheet feeding device 1 further includes the hopper 2 onwhich sheet S are stacked, and the separation roller 31 separates thesheet S stacked on the hopper 2 one by one to feed the separated sheet Ssequentially. The following roller 6 is arranged on the upstream side ofthe separation roller 31 in the feeding direction Y. Therefore, anacceleration acting on the following roller 6 and the roller supportingmechanism 7, which move along with a behavior of the sheet S, can bemeasured at an appropriate position where a change in the behavior ofthe sheet S appears mostly. Consequently, it is possible to detect afeed error of the sheet S more reliably.

Moreover, the feeding stop unit 46 stops the feeding of the sheet S bythe separate-feeding unit 3 depending on a result of the detection bythe error detecting unit 44. In other words, when the error detectingunit 44 detects a feed error of the sheet S, the feeding stop unit 46stops the feeding of the sheet S by the separate-feeding unit 3.Therefore, it is possible to prevent a damage to the sheet S fromoccurring.

In the first embodiment, the sheet feeding device 1 is applied to theimage reading apparatus; however, the sheet feeding device 1 can beapplied to any other apparatuses.

Furthermore, in the first embodiment, the following roller 6 that has acylindrical shape and rolls by having line contact with a sheet S on aline along the width direction X is used. As long as it is possible torotate around an axis in the height direction Z by the action of amoment of rotation around the axis in the height direction Z, any shapeof a rotating body can be used instead of the following roller 6. Forexample, a pair of disks which rotation axes are connected to each othercan be used. In this case, the disks respectively have point contactwith the sheet S at a plurality of points (two points) along the widthdirection X.

Moreover, the following roller 6 is arranged on the downstream side of adownstream-side edge (a leading edge) of each of sheets S stacked on thestacking surface 21 in the feeding direction Y. Therefore, it is alsopossible to detect a so-called a leading-edge skew occurring in such acase that a sheet S is set up askew from the beginning. In this case,when the feeding of the sheet S set up askew from the beginning isstarted, there is a time lag in a timing of contact with the sheet Samong portions of the following roller 6, i.e., the following roller 6supposed to have line contact with the sheet S on a line along the widthdirection X has contact with the sheet S at a different timing dependingon portions of the following roller 6. Due to a difference in africtional force generated between the following roller 6 and the sheetS depending on portions of the following roller 6 along the widthdirection X, a moment of rotation around an axis in the height directionZ acts on the following roller 6, so that the following roller 6 rollsaround the axis in the height direction Z. Therefore, the errordetecting unit 44 can detect a leading-edge skew based on anacceleration acting on the three-axis accelerometer 8. In other words,it is also possible to detect a leading-edge skew with the three-axisaccelerometer 8.

Furthermore, in the first embodiment, the error detecting unit 44detects a skew or a jam when an increase or decrease of an accelerationsensed by the three-axis accelerometer 8 is continued for thepredetermined time period. Alternatively, a threshold with respect to anacceleration sensed by the three-axis accelerometer 8 can be set up sothat the error detecting unit 44 simply detects a skew or a jam when theacceleration exceeds the threshold.

Moreover, the error detecting unit 44 can detect a status of a feederror of the sheet S in detail based on a combination of accelerationsGx, Gy, and Gz in three directions measured by the three-axisaccelerometer 8. In addition, a status of a feed error of the sheet Scan be detected in more detail based on a temporal change in each of theaccelerations Gx, Gy, and Gz. Furthermore, in the first embodiment, thefeeding stop unit 46 stops the feeding of the sheet S when the errordetecting unit 44 detects a feed error of the sheet S. Alternatively,depending on a more-detailed status of a feed error of the sheet S, anerror process can be arbitrarily set up.

FIGS. 8A to 8C are respectively a plan view, a front view, and a sideview of an acceleration detecting unit 205 of a sheet feeding device 201according to a second embodiment of the present invention. The portionsor components identical to those for the first embodiment are denotedwith the same reference numerals, and the detailed description of thoseportions or components will not be repeated here. A difference betweenthe sheet feeding devices 1 and 201 is that the sheet feeding device 201includes the acceleration detecting unit 205 instead of the accelerationdetecting unit 5.

The acceleration detecting unit 205 includes the following roller 6, aroller supporting mechanism 207, and the three-axis accelerometer 8. Thefollowing roller 6 rolls by having contact with a sheet S being fed. Theroller supporting mechanism 207 supports the following roller 6. Thethree-axis accelerometer 8 measures an acceleration acting on the rollersupporting mechanism 207.

The roller supporting mechanism 207 rotatably supports the followingroller 6 so that the following roller 6 can roll in the feedingdirection Y at a predetermined position. The roller supporting mechanism207 can move in the height direction Z and rotate around an axis alongthe height direction Z along with a behavior of the sheet S, at least.The roller supporting mechanism 207 includes the roller support shaft71, the bracket 72, a roller supporting member 273, the roller-sidecoupling member 74, and a supporting-member-side coupling member 275.

The roller supporting member 273 includes a support plate 273 a and aguide shaft 273 b. The support plate 273 a is fixed to, for example, acasing (not shown) of the sheet feeding device 201. The guide shaft 273b has a rod-like shape. A base end of the guide shaft 273 b is fixed tothe support plate 273 a so that the guide shaft 273 b extends downwardfrom the support plate 273 a in the height direction Z. Thesupporting-member-side coupling member 275 has a guide hole 275 aextending in the height direction Z. A leading end of the guide shaft273 b is inserted into the guide hole 275 a. The supporting-member-sidecoupling member 275 can move in the height direction Z with being guidedby the guide shaft 273 b. The supporting-member-side coupling member 275and the roller-side coupling member 74 are rotatably coupled to eachother via the feeding-directional shaft 78.

Therefore, the roller supporting mechanism 207 can move up and down inthe height direction Z along the guide shaft 273 b together with thefollowing roller 6. When there is a change in a behavior of the sheet Sdue to uplift of the sheet S, and a force generated by the uplift of thesheet S acts on the following roller 6 and the roller supportingmechanism 207, the roller supporting mechanism 207 moves in the heightdirection Z along with the behavior of the sheet S together with thefollowing roller 6. When there is a change in a behavior of the sheet Sdue to an occurrence of a cumulative skew of the sheet S, and a momentof rotation around an axis in the height direction Z acts on thefollowing roller 6 and the roller supporting mechanism 207, the rollersupporting mechanism 207 rotates around the guide shaft 273 b as arotating shaft together with the following roller 6.

In this manner, the sheet feeding device 201 includes the followingroller 6 capable of rolling by having line contact with a sheet S fed bythe separate-feeding unit 3 on a line along the width direction X of thesheet S, the roller supporting mechanism 207 that supports the followingroller 6 so that the following roller 6 can roll in the feedingdirection Y at the predetermined position on the sheet S, and is capableof moving and rotating along with a behavior of the sheet S fed by theseparate-feeding unit 3 together with the following roller 6, thethree-axis accelerometer 8 capable of measuring accelerations in threedirections acting on the roller supporting mechanism 207, and the errordetecting unit 44 that detects a feed error of the sheet S based on theaccelerations measured by the three-axis accelerometer 8.

Specifically, the error detecting unit 44 detects a feed error of thesheet S based on accelerations Gx, Gy, and Gz in the width direction X,the feeding direction Y, and the height direction Z, respectively, whichact on the roller supporting mechanism 207 capable of moving androtating along with a behavior of the sheet S together with thefollowing roller 6. In this manner, with only one sensor, i.e., thethree-axis accelerometer 8, behaviors of the following roller 6 and theroller supporting mechanism 207 can be sensed, and thereby sensing abehavior of the sheet S indirectly. Therefore, the sheet feeding device201 can detect a plurality of types of feed errors separately with acompact and simple configuration.

FIGS. 9 and 10 are respectively a plan view and a side view of a sheetfeeding device 301 according to a third embodiment of the presentinvention. The portions or components identical to those for the firstembodiment are denoted with the same reference numerals, and thedetailed description of those portions will not be repeated here. Adifference between the sheet feeding devices 1 and 301 is that the sheetfeeding device 301 includes an acceleration detecting unit 305 insteadof the acceleration detecting unit 5.

A difference between the acceleration detecting units 5 and 305 is thatthe acceleration detecting unit 305 further includes an arm member 309.

A base end of the arm member 309 is fixed to the coupling plate 74 a,and the three-axis accelerometer 8 is arranged on a leading end of thearm member 309. The arm member 309 has a rod-like shape extending on thedownstream side in the feeding direction Y when the following roller 6and the roller supporting mechanism 7 are located in a proper position.The three-axis accelerometer 8 is arranged on the leading end of the armmember 309, i.e., the three-axis accelerometer 8 is arranged relativelyfar away from the rotating shaft of the following roller 6 and theroller supporting mechanism 7 that move along with the sheet S whenthere is a change in a behavior of the sheet S. Therefore, a radius ofrotation of the three-axis accelerometer 8, which moves along with thefollowing roller 6 and the roller supporting mechanism 7 when there is achange in a behavior of the sheet S, can be relatively long, and therebyincreasing a moving amount of the three-axis accelerometer 8. As aresult, even when there is a small change in a behavior of the sheet S,an acceleration acting on the three-axis accelerometer 8 can beamplified mechanically by the action of the arm member 309.Consequently, the three-axis accelerometer 8 can be sensitive to aslight movement of the sheet S as if there were a great change in abehavior of the sheet S, and a measurement value (an output value) ofthe three-axis accelerometer 8 can be amplified mechanically.

In this manner, the sheet feeding device 301 includes the followingroller 6 capable of rolling by having line contact with a sheet S fed bythe separate-feeding unit 3 on a line along the width direction X of thesheet S, the roller supporting mechanism 7 that supports the followingroller 6 so that the following roller 6 can roll in the feedingdirection Y at the predetermined position on the sheet S, and is capableof moving and rotating along with a behavior of the sheet S fed by theseparate-feeding unit 3 together with the following roller 6, thethree-axis accelerometer 8 capable of measuring accelerations in threedirections acting on the roller supporting mechanism 7, and the errordetecting unit 44 that detects a feed error of the sheet S based on theaccelerations measured by the three-axis accelerometer 8.

Specifically, the error detecting unit 44 detects a feed error of thesheet S based on accelerations Gx, Gy, and Gz in the width direction X,the feeding direction Y, and the height direction Z, respectively, whichact on the roller supporting mechanism 7 capable of moving and rotatingalong with a behavior of the sheet S together with the following roller6. In this manner, with only one sensor, i.e., the three-axisaccelerometer 8, behaviors of the following roller 6 and the rollersupporting mechanism 7 can be sensed, and thereby sensing a behavior ofthe sheet S indirectly. Therefore, the sheet feeding device 301 candetect a plurality of types of feed errors separately with a compact andsimple configuration.

Furthermore, the sheet feeding device 301 further includes the armmember 309. The base end of the arm member 309 is fixed to the rollersupporting mechanism 7, and the three-axis accelerometer 8 is arrangedon the leading end of the arm member 309. Therefore, even when there isa small change in a behavior of the sheet S, an acceleration acting onthe three-axis accelerometer 8 can be amplified by the action of the armmember 309. Consequently, the three-axis accelerometer 8 can besensitive to a slight movement of the sheet S as if there were a greatchange in a behavior of the sheet S, and a measurement value (an outputvalue) of the three-axis accelerometer 8 can be amplified mechanically,so that it is possible to detect a feed error of the sheet S morereliably.

FIG. 11 is a block diagram of a sheet feeding device 401 according to afourth embodiment of the present invention. The portions or componentsidentical to those for the second embodiment are denoted with the samereference numerals, and the detailed description of those portions orcomponents will not be repeated here. A difference between the sheetfeeding devices 201 and 401 is that the sheet feeding device 401includes an acceleration detecting unit 405 instead of the accelerationdetecting unit 205. FIG. 12 is a perspective view of the accelerationdetecting unit 405.

The acceleration detecting unit 405 includes a following roller 406, aroller supporting mechanism 407, the three-axis accelerometer 8, and avibration applying unit 410. The following roller 406 rolls by havingcontact with a sheet S being fed. The roller supporting mechanism 407supports the following roller 406.

As shown in FIG. 12, the roller supporting mechanism 407 rotatablysupports the following roller 406 so that the following roller 406 canroll in the feeding direction Y at a predetermined position. The rollersupporting mechanism 407 can move in the height direction Z and rotatearound an axis along the height direction Z along with a behavior of thesheet S, at least. The roller supporting mechanism 407 includes a rollersupport shaft 471, a guide-shaft supporting member 473, and aroller-side support shaft 479.

The roller support shaft 471 is arranged along the width direction X,and serves as a rotating shaft of the following roller 406. Theguide-shaft supporting member 473 includes a support plate 473 a and aguide shaft 473 b. The support plate 473 a is fixed to, for example, acasing (not shown) of the sheet feeding device 401. The guide shaft 473b has a rod-like shape. A base end of the guide shaft 473 b is fixed tothe support plate 473 a so that the guide shaft 473 b extends downwardfrom the support plate 473 a in the height direction Z. One end of theroller-side support shaft 479 is integrally connected to one end of theroller support shaft 471. A guide hole 479 a extending in the heightdirection Z is formed on the other end of the roller-side support shaft479. A leading end of the guide shaft 473 b is inserted into the guidehole 479 a. The roller-side support shaft 479 can move in the heightdirection Z with being guided by the guide shaft 473 b along withbehaviors of the roller support shaft 471 and the following roller 406.

In other words, the roller supporting mechanism 407 can move up and downin the height direction Z along the guide shaft 473 b together with thefollowing roller 406. When there is a change in a behavior of the sheetS due to uplift of the sheet S, and a force generated by the uplift ofthe sheet S acts on the following roller 406 and the roller supportingmechanism 407, the roller supporting mechanism 407 moves in the heightdirection Z along with the behavior of the sheet S together with thefollowing roller 406. When there is a change in a behavior of the sheetS due to an occurrence of a cumulative skew of the sheet S, and a momentof rotation around the axis in the height direction Z acts on thefollowing roller 406 and the roller supporting mechanism 407, the rollersupporting mechanism 407 rotates around the guide shaft 473 b as therotating shaft together with the following roller 406.

The vibration applying unit 410 applies a periodical vibration in theheight direction Z to the three-axis accelerometer 8. The vibrationapplying unit 410 includes an eccentric cam groove 411, a slide shaft412, and a slide guide 413. The eccentric cam groove 411 is formed on aside surface of the following roller 406 as a concave groove. Theeccentric cam groove 411 is an annular groove which center is arrangedwith a shift of a predetermined distance from a central axis of theroller support shaft 471. In other words, the center of the eccentriccam groove 411 is eccentrically arranged with respect to the rotatingshaft of the following roller 406. The slide shaft 412 has a rod-likeshape, and a protruding portion 414 is formed on one end of the slideshaft 412. The slide guide 413 is fixed to, for example, the casing (notshown) of the sheet feeding device 401. The protruding portion 414 isinserted into the eccentric cam groove 411, and the other end of theslide shaft 412 is inserted into the slide guide 413, so that the slideshaft 412 is reciprocatably supported by the slide guide 413 so that theslide shaft 412 can reciprocate in the height direction Z. Thethree-axis accelerometer 8 is arranged on the other end of the slideshaft 412.

As the following roller 406 rolls by having contact with the sheet Sbeing fed, the protruding portion 414 is guided along the eccentric camgroove 411, so that the slide shaft 412 reciprocates up and down in theheight direction Z. In this manner, a periodical vibration in the heightdirection Z can be applied to the three-axis accelerometer 8 arranged onthe end of the slide shaft 412. As a result, a measurement value of anacceleration Gz with a certain periodicity can be obtained from thethree-axis accelerometer 8. In other words, the three-axis accelerometer8 is periodically vibrated in the height direction Z in a positive way,so that it is possible to obtain a measurement value of the accelerationGz with a stable period, phase, and amplitude depending on a feedingspeed of the sheet S when the sheet S is fed properly. Therefore, it ispossible to grasp a feeding status of the sheet S in more detail.

Specifically, as shown in FIG. 11, the processing unit 41 of the sheetfeeding device 401 further includes a waveform generating unit 447 and acomparing unit 448. The waveform generating unit 447 generates anacceleration waveform of an acceleration in the height direction Z basedon a measurement value of the acceleration Gz in the height direction Z.In this case, the acceleration waveform indicates an actually measuredacceleration Gz with respect to a time T. The storing unit 42 of thesheet feeding device 401 stores therein a reference accelerationwaveform depending on a feeding speed. The reference accelerationwaveform is a reference waveform of an acceleration in the heightdirection Z depending on a feeding speed of the sheet S fed by theseparate-feeding unit 3. For example, when a fluctuation in rolling ofthe following roller 406 occurs due to a jam or the like, theacceleration waveform generated by the waveform generating unit 447 doesnot match with the reference acceleration waveform. FIG. 13 is a graphof an example of an acceleration waveform of an acceleration in theheight direction Z when no feed error occurs. FIG. 14 is a graph of anexample of an acceleration waveform of an acceleration in the heightdirection Z when a feed error occurs. As shown in FIG. 13, when no feederror occurs, the acceleration waveform indicates a periodical waveformpattern matching with the reference acceleration waveform. On the otherhand, as shown in FIG. 14, when a feed error occurs, the accelerationwaveform indicates a nonperiodical waveform pattern or a scatteringamplitude. Therefore, it is possible to grasp a feeding status of thesheet S in more detail based on a plurality of parameters for, forexample, a period, an amplitude, and a phase of an acceleration waveformof the acceleration Gz. The comparing unit 448 compares an accelerationwaveform generated by the waveform generating unit 447 with thereference acceleration waveform. The error detecting unit 44 of thesheet feeding device 401 detects a feed error of the sheet S based on aresult of the comparison by the comparing unit 448.

A feed-error detecting process performed by the sheet feeding device 401is explained in detail below with reference to a flowchart shown in FIG.15. The control unit 4 determines whether a sheet S is being fed at thismoment (Step S400). If the sheet S is not being fed at this moment (NOat Step S400), the counting unit 45 clears all values of each ofcounters for accelerations in each direction, and the feed-errordetecting process is terminated as a normal end. If the sheet S is beingfed at this moment (YES at Step S400), the control unit 4 selects areference acceleration waveform depending on a feeding speed of thesheet S from those stored in the storing unit 42 (Step S402).

The control unit 4 acquires accelerations Gx, Gy, and Gz respectively inthe width direction X, the feeding direction Y, and the height directionZ that are measured at predetermined sampling intervals by thethree-axis accelerometer 8 (Step S404), and stores the acquiredaccelerations Gx, Gy, and Gz in a time trace buffer (not shown) of thestoring unit 42 (Step S406). The waveform generating unit 447 generatesan acceleration waveform of the acceleration in the height direction Zbased on a measurement value of the acceleration Gz (Step S408).

The comparing unit 448 compares the acceleration waveform generated atStep S408 with the reference acceleration waveform selected at StepS402, and the control unit 4 determines whether an amplitude of thegenerated acceleration waveform matches with that of the referenceacceleration waveform based on a result of the comparison by thecomparing unit 448 (Step S410). For example, when a difference betweenthe amplitudes of the generated acceleration waveform and the referenceacceleration waveform exceeds an amplitude difference threshold, thecontrol unit 4 determines that the generated acceleration waveform doesnot match with the reference acceleration waveform. If it is determinedthat the amplitude of the generated acceleration waveform does not matchwith that of the reference acceleration waveform (NO at Step S410), theerror detecting unit 44 detects a feed error of the sheet S, and aserror processes, the control unit 4 informs a user of an error, and thefeeding stop unit 46 stops the feeding of the sheet S (Step S412). Then,the feed-error detecting process is terminated as an abnormal end.

If it is determined that the amplitude of the generated accelerationwaveform matches with that of the reference acceleration waveform (YESat Step S410), the comparing unit 448 compares the acceleration waveformgenerated at Step S408 with the reference acceleration waveform selectedat Step S402, and the control unit 4 determines whether a period of thegenerated acceleration waveform is delayed in comparison with that ofthe reference acceleration waveform based on a result of the comparisonby the comparing unit 448 (Step S414). For example, when a delay in theperiod of the generated acceleration waveform in comparison with that ofthe reference acceleration waveform exceeds a period delay threshold,the control unit 4 determines that the period of the generatedacceleration waveform is delayed in comparison with that of thereference acceleration waveform. If it is determined that the period ofthe generated acceleration waveform is delayed in comparison with thatof the reference acceleration waveform (YES at Step S414), it can beassumed that the feeding speed of the sheet S is decreased, so that theerror detecting unit 44 forecasts an occurrence of a jam before the jamoccurs, and as error processes, the control unit 4 informs a user of anerror, and the feeding stop unit 46 stops the feeding of the sheet S(Step S416). Then, the feed-error detecting process is terminated as theabnormal end.

If it is determined that the period of the generated accelerationwaveform is not delayed in comparison with that of the referenceacceleration waveform (NO at Step S414), the control unit 4 compares thecurrently-acquired accelerations Gx, Gy, and Gz with previously-acquiredaccelerations Gx, Gy, and Gz (Step S418), and the counting unit 45determines whether the currently-acquired acceleration Gy increases (ordecreases) as compared with the previously-acquired acceleration Gy(Step S420). If it is determined that the acceleration Gy increases (ordecreases) (YES at Step S420), the counting unit 45 increments a valueof a counter for the acceleration Gy by one. The error detecting unit 44determines whether the increase (or decrease) of the acceleration Gy iscontinued for the predetermined time period based on whether theincremented value of the counter for the acceleration Gy reaches orexceeds a threshold (Step S422). If the error detecting unit 44determines that the increase (or decrease) of the acceleration Gy iscontinued for the predetermined time period (YES at Step S422), anddetects a skew of the sheet S, as error processes, the control unit 4informs a user of an error, and the feeding stop unit 46 stops thefeeding of the sheet S (Step S424). Then, the feed-error detectingprocess is terminated as the abnormal end.

If it is determined that the acceleration Gy does not increase (ordecrease) (NO at Step S420), or if it is determined that the increase(or decrease) of the acceleration Gy is not continued for thepredetermined time period (NO at Step S422), the counting unit 45determines whether the currently-acquired acceleration Gx increases (ordecreases) as compared with the previously-acquired acceleration Gx(Step S426). If it is determined that the acceleration Gx increases (ordecreases) (YES at Step S426), the counting unit 45 increments a valueof a counter for the acceleration Gx by one. The error detecting unit 44determines whether the increase (or decrease) of the acceleration Gx iscontinued for the predetermined time period based on whether theincremented value of the counter for the acceleration Gx reaches orexceeds a threshold (Step S428). If the error detecting unit 44determines that the increase (or decrease) of the acceleration Gx iscontinued for the predetermined time period (YES at Step S428), anddetects a skew of the sheet S, as error processes, the control unit 4informs a user of an error, and the feeding stop unit 46 stops thefeeding of the sheet S (Step S430). Then, the feed-error detectingprocess is terminated as the abnormal end. If it is determined that theacceleration Gx does not increase (or decrease) (NO at Step S426), or itis determined that the increase (or decrease) of the acceleration Gx isnot continued for the predetermined time period (NO at Step S428), theprocess control returns to Step S400.

In this manner, the sheet feeding device 401 includes the followingroller 406 capable of rolling by having line contact with a sheet S fedby the separate-feeding unit 3 on a line along the width direction X ofthe sheet S, the roller supporting mechanism 407 that supports thefollowing roller 406 so that the following roller 406 can roll in thefeeding direction Y at the predetermined position on the sheet S, and iscapable of moving and rotating along with a behavior of the sheet S fedby the separate-feeding unit 3 together with the following roller 406,the three-axis accelerometer 8 capable of measuring accelerations inthree directions acting on the roller supporting mechanism 407, and theerror detecting unit 44 that detects a feed error of the sheet S basedon the accelerations measured by the three-axis accelerometer 8.

Specifically, the error detecting unit 44 detects a feed error of thesheet S based on accelerations Gx, Gy, and Gz in the width direction X,the feeding direction Y, and the height direction Z, respectively, whichact on the roller supporting mechanism 407 capable of moving androtating along with a behavior of the sheet S together with thefollowing roller 406. In this manner, with only one sensor, i.e., thethree-axis accelerometer 8, behaviors of the following roller 406 andthe roller supporting mechanism 407 can be sensed, and thereby sensing abehavior of the sheet S indirectly. Therefore, the sheet feeding device401 can detect a plurality of types of feed errors separately with acompact and simple configuration.

Furthermore, the sheet feeding device 401 includes the vibrationapplying unit 410 that applies a periodical vibration in the heightdirection Z to the three-axis accelerometer 8, the waveform generatingunit 447 that generates an acceleration waveform of an acceleration inthe height direction Z based on a measurement value of the accelerationGz in the height direction Z, the storing unit 42 that stores therein areference acceleration waveform as a reference of an accelerationwaveform in the height direction Z depending on a feeding speed of thesheet S fed by the separate-feeding unit 3, and the comparing unit 448that compares the acceleration waveform generated by the waveformgenerating unit 447 with the reference acceleration waveform. The errordetecting unit 44 detects a feed error of the sheet S based on a resultof the comparison by the comparing unit 448. Therefore, the three-axisaccelerometer 8 is periodically vibrated in the height direction Z in apositive way, so that it is possible to obtain a measurement value ofthe acceleration Gz with a stable period, phase, and amplitude.Consequently, it is possible to grasp a feeding status of the sheet S inmore detail based on a plurality of parameters for, for example, aperiod, an amplitude, and a phase of an acceleration waveform of theacceleration Gz.

Incidentally, the vibration applying unit 410 including the eccentriccam groove 411, the slide shaft 412, and the slide guide 413 is employedin the fourth embodiment. As long as it is possible to apply aperiodical vibration in the height direction Z to the three-axisaccelerometer 8, a vibration applying unit with a differentconfiguration can be employed.

According to the embodiments of the present invention, a sheet feedingdevice detects a feed error of a sheet based on accelerations in threedirections (or dimensions) acting on a supporting member capable ofmoving and rotating along with a behavior of the sheet together with arolling member. Therefore, with a compact and simple configuration, itis possible to detect a plurality of types of feed errors occurringwhile the sheet is being fed before a damage to the sheet due to thefeed error occurs.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

1. A sheet feeding device comprising: a feeding unit that feeds a sheet;a rolling member that rolls by having contact with the sheet being fedby the feeding unit; a supporting member that moves along with abehavior of the sheet with supporting the rolling member so that therolling member rolls in a feeding direction of the sheet at apredetermined position on the sheet; an acceleration measuring unit thatmeasures accelerations acting on the supporting member in threedirections; and a detecting unit that detects a feed error of the sheetbased on the accelerations measured by the acceleration measuring unit.2. The sheet feeding device according to claim 1, wherein theacceleration measuring unit measures accelerations in the feedingdirection, a width direction horizontally-perpendicular to the feedingdirection, and a height direction perpendicular to both the feedingdirection and the width direction, and the supporting member moves inthe height direction and rotates around an axis along the heightdirection along with the behavior of the sheet.
 3. The sheet feedingdevice according to claim 2, wherein the detecting unit detects a skewof the sheet as a feed error of the sheet when an increase or decreaseof any of the accelerations in the feeding direction and the widthdirection is continued for a predetermined time period.
 4. The sheetfeeding device according to claim 2, wherein the detecting unit detectsa jam of the sheet as a feed error of the sheet when an increase ordecrease of the acceleration in the height direction is continued for apredetermined time period.
 5. The sheet feeding device according toclaim 2, further comprising a vibration applying unit that applies aperiodical vibration in the height direction to the accelerationmeasuring unit; a waveform generating unit that generates anacceleration waveform of the acceleration in the height direction basedon a result of measurement by the acceleration measuring unit; a storingunit that stores therein a reference acceleration waveform as areference of the acceleration waveform in the height direction dependingon a feeding speed of the sheet fed by the feeding unit; and a comparingunit that compares the acceleration waveform generated by the waveformgenerating unit with the reference acceleration waveform, wherein thedetecting unit detects a feed error of the sheet based on a result ofcomparison by the comparing unit.
 6. The sheet feeding device accordingto claim 1, wherein the rolling member has a cylindrical shape, and arotating shaft of the rolling member is arranged along the widthdirection.
 7. The sheet feeding device according to claim 1, furthercomprising an arm member having a base end portion and a leading endportion, wherein the base end portion of the arm member is fixed to thesupporting member and the acceleration measuring unit is provided on theleading end portion of the arm member.
 8. The sheet feeding deviceaccording to claim 1, further comprising a stacking member on which aplurality of sheets are stacked, wherein the feeding unit includes aseparating unit that separates the sheets stacked on the stacking memberone by one, and the rolling member is arranged on an upstream side ofthe separating unit in the feeding direction.
 9. The sheet feedingdevice according to claim 1, further comprising a feeding stop unit thatstops a feeding of the sheet by the feeding unit depending on a resultof detection by the detecting unit.
 10. The sheet feeding deviceaccording to claim 1, wherein the rolling member has point contact withthe sheet at a plurality of points located along a width directionhorizontally-perpendicular to the feeding direction.
 11. The sheetfeeding device according to claim 1, wherein the rolling member has linecontact with the sheet on a line along a width directionhorizontally-perpendicular to the feeding direction.